The gunman accused of targeting and murdering 10 Black people at a supermarket in Buffalo, New York, was indicted by a grand jury on a slew of federal hate crime and firearm charges on Thursday, the Department of Justice announced. 

Payton Gendron, who was 18 years old at the time of the shooting, faces life in prison or the death penalty if convicted. 

The indictment comes about one month after federal hate crime charges were announced. He has also pleaded not guilty to 25 state charges, including murder, attempted murder, and domestic terrorism. 

Prosecutors say that Gendron planned the attack for months and was motivated by racist beliefs. FBI agents found a note at his home the day after the shooting in which he said he "had to commit this attack" because he cares "for the future of the White race," according to an affidavit. 

Buffalo shooting suspect Payton Gendron

Buffalo shooting suspect, Payton S. Gendron, who is accused of killing 10 people in a live-streamed supermarket shooting in a Black neighborhood of Buffalo, is escorted in the courtroom in shackles, in Buffalo, New York, U.S., May 19, 2022. (Reuters/Brendan McDermid)

The gun that Gendron allegedly used, a Bushmaster XM rifle, had racial slurs scribbled on it, as well as, "Here’s your reparations!" and the names of other people who have committed mass shootings

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A diary he kept also included "statements that his motivation for the attack was to prevent Black people from replacing white people and eliminating the white race, and to inspire others to commit similar racially-motivated attacks," according to a criminal complaint. 

"The Justice Department fully recognizes the threat that white supremacist violence poses to the safety of the American people and American democracy," Attorney General Merrick Garland said in a statement on Thursday. "We will continue to be relentless in our efforts to combat hate crimes, to support the communities terrorized by them, and to hold accountable those who perpetrate them."

Garland will determine at a later date whether to seek the death penalty. Gendron's attorneys have said in court that federal prosecutors told them it could take a year before the decision on the death penalty is made. 

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The Tops Friendly Supermarket where the shooting took place, meanwhile, reopened on Thursday for the first time since the shooting on May 14. 

The Associated Press contributed to this report.